Endocrine Abstracts

Subclinical hyperthyroidism is a biochemical diagnosis defined with suppressed levels of TSH and normal levels of thyroid hormones. One of the main metabolic responses to thyroid hyperfunction is peripheral lipolysis and release of free fatty acids (FFA). The aim of this study was to compare levels of cholesterol, LDL, HDL and triglycerides in persons with subclinical hyperthyroidism to age and BMI matched euthyroid healthy control. We evaluated 45 persons in two groups: 1st group: 30 patients (26 women and 4 men) with subclinical hyperthyroidism, mean age 49.13±10.21 years, mean BMI 25.18±4.04 kg/m², with laboratory proven subclinical hyperthyroidism. Second group: 15 healthy euthyroid controls, mean age 49.40±9.84 years, mean BMI 23.74±4.09 kg/m². None of them had a history of coronary heart disease, signs of liver and/or renal dysfunction or were previously treated with lipid lowering drugs. Statistical analysis was performed with t-test. In the 1st group, mean cholesterol level was 6.15±1.10 mmol/l, mean LDL level was 4.08±0.96 mmol/l, mean HDL level was 1.46±0.49 mmol/l and mean triglycerides level was 1.71±0.57 mmol/l. In the 2nd group, mean cholesterol level was 5.38±1.03 mmol/l, mean LDL was 3.16±0.68 mmol/l, mean HDL level was 1.37±0.37 mmol/l and mean triglycerides level was 1.29±0.55 mmol/l. There was a significant difference in levels of cholesterol (P<0.05; P=0.035) and triglycerides (P<0.05; P=0.0034) and the difference in LDL was high (P<0.01; P=0.005). There was no difference in HDL levels (P>0.05; P=0.55). The clinical presentation of subclinical hyperthyroidism is quite subtle which points to not so high metabolic rate of this condition and no real metabolic need for utilization of released FFA’s. This may be the possible explanation for unexpected and surprising result of hyperlipidemia in subclinical hyperthyroidism.